This invention generally relates to fusing members and, more specifically, the present invention relates to fuser roll functional release agents that, for example, enhance release of toner from a fuser roll. In embodiments, the release agent of the present invention is comprised of a hydride (SiH) functional oil that prevents offset by providing a coating on a fuser roll substrate, and which coating contains a filler that has been reacted with the silicone hydride oil preferably in the presence of a catalyst; and the use of reacted hydride functional oils as a functional release agent that prevents offsetting by providing a silicone coating on exposed high energy surfaces in oxidized or high filler content siloxane fuser rolls. Advantages of the fuser members of the present invention include avoiding or minimizing offsetting, improved fusing latitude, reduction in offsetting from preprinted forms, high thermal conductivity, and providing a siloxane release surface in those areas of a silicone coating that would normally have unacceptable high surface energy, and thus poor release. In embodiments, the release coatings of the present invention can be obtained by combining a hydride functional siloxane with active functional groups on filler components thereby providing a low surface energy silicone surface over the filler. The fuser members of the present invention, which can be selected for a number of known electrophotographic imaging and printing processes, possess a number of advantages as indicated herein, such as the elimination, or minimization of offsetting observed when fillers are used alone and not reacted with a silicone hydride release oil. The types of components such as rolls that can be provided with the coatings of the present invention are illustrated, for example, in U.S. Pat. Nos. 4,373,239 and 4,518,655, the disclosures of which are totally incorporated herein by reference.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which may be the photosensitive member itself or other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is know. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner composition to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member, such as paper. Thereafter, as the toner cools, solidification of the toner causes it to be firmly bonded to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 90.degree. C. to about 160.degree. C. or higher depending upon the softening range of the particular resin used in the toner. It is undesirable, however, to raise the temperature of the substrate substantially higher than about 200.degree. C. because, for example, of the tendency of the substrate to discolor at such elevated temperatures, particularly when the substrate is paper.
Several methods for the thermal fusing of electroscopic toner images have been described in the prior art. These methods include the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner results when the proper combination of heat, pressure and contact time are provided.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, plate, or belt members. The concurrent transfer of heat and the application of pressure in the nip effects the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied. This is referred to as "hot offset" and occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser roll, and accordingly it is desirable to provide a fusing surface which has a low surface energy to provide the necessary effective release. To insure and maintain good release properties of the fuser roll, it has become customary to apply release agents to the fuser members to insure that the toner is completely released from the fuser roll during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils to prevent toner offset.
Described in U.S. Pat. Nos. 4,264,181, 4,257,699 and 4,272,179, all commonly assigned to the assignee of the present application, the disclosures of which are totally incorporated herein by reference, are fuser members and certain release agents. These patents describe specific fuser members and methods of fusing thermoplastic resin toner images to a substrate wherein a certain polymeric release agent having functional groups is applied to the surface of the fuser member. The fuser member comprises a base member having an elastomeric surface with a metal containing filler therein which has been cured with a nucleophilic addition curing agent. Exemplary of such a fuser member is an aluminum base member with a poly(vinylidenefluoride-hexafluoropropylene) copolymer cured with a bisphenol curing agent having lead oxide filler dispersed therein and utilizing a mercapto functional polyorgano siloxane oil as a release agent. In these fusing processes, the polymeric release agents have functional groups, also designated as chemically reactive functional groups, which interact with the metal containing filler dispersed in the elastomer or resinous material of the fuser member surface to form a thermally stable film which releases thermoplastic resin toner and which prevents the thermoplastic resin toner from contacting the elastomer material itself. The metal oxide, metal salt, metal alloy or other suitable metal compound filler dispersed in the elastomer or resin upon the fuser member surface interacts with the functional groups of the siloxane polymeric release agent. Preferably, the metal containing filler materials do not cause degradation of or have any adverse effect upon the polymeric release agent having functional groups. Because of this reaction between the elastomer having a metal containing filler and the polymeric release agent having functional groups, excellent release and the production of high quality copies are obtained even at high rates of speed of electrostatographic reproducing machines. With these VITON.RTM./lead oxide, or VITON.RTM./copper oxide members, an oxide of low volume fraction is added to enable a specific functional release agent to react with it and thereby coat the silicone polymer oil like a polysiloxane, while with the present invention in embodiments the fillers, which are preferably selected in amounts of from about 55 to 70 volume percent based on amount of silicone rubber, are covered with a silicone hydride oil, rather than the polysiloxane oil. Thus, with the present invention improved toner and oil release is achieved from the fuser roll.
While the mechanism involved is not completely understood, it has been observed in embodiments of the present invention that when certain polymeric fluids having functional groups are applied to the surface of a fusing member having an elastomer surface with a metal oxide, metal salt, metal, metal alloy or other suitable metal compounds dispersed therein there is an interaction, a chemical reaction, coordination complex, hydrogen bonding or other mechanism between the active functional groups, like oxides, hydroxyls, halides, carboxylics, and the like, of the filler in the elastomer and the polymeric fluid having functional groups so that the polymeric release .agent having functional groups in the liquid provide an excellent surface for release having an excellent propensity to remain upon the surface of the fuser member. There appears, however, to be the formation of a film upon the elastomer surface which differs from the composition of the elastomer and the composition of the polymeric release agent having functional groups. This film, however, has a greater affinity for the elastomer containing a metal compound than the toner and thereby provides an excellent release coating upon the elastomer surface. The release coating has a cohesive force which is less than the adhesive forces between heated toner and the substrate to which it is applied and the cohesive forces of the toner. The interaction between the functional group of the polymeric release agent and the fillers in the elastomer results in an overall diminution of the critical or high surface energy of the fillers.
The use of polymeric release agents having functional groups, which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having superior release properties for electroscopic thermoplastic resin toners, is described in U.S. Pat. Nos. 4,029,827; 4,101,686 and 4,185,140, all commonly assigned to the assignee of the present invention. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorgano siloxanes having mercapto functionality as release agents. U.S. Pat. Nos. 4,101,686 and 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether and mercapto groups as release fluids.